(tr)uSDX bootloader corruption – a smoking gun – an experiment

At (tr)uSDX bootloader corruption – a smoking gun I proposed that the (tr)uSDX (trusdx) is vulnerable to users attempting to program the initial bootloader file using the (tr)uSDX USB port and its bootloader interface because without protection, that will attempt to overlay the bootloader while it is being executed and that is likely to corrupt the bootloader.

The (tr)uSDX bootloader code is proprietary, ie secret.

This article documents an experiment that demonstrates the vulnerability, and the effect of bootloader section protection.

Below are a series of verbose AVRDUDE logs of the operations to discover / demonstrate the outcomes. Continue reading (tr)uSDX bootloader corruption – a smoking gun – an experiment

Last update: 25th July, 2022, 1:19 PM

(tr)uSDX bootloader corruption – a smoking gun

A common topic of discussion on (tr)uSDX (trusdx) forum is problems in loading firmware (application or bootloader.

A user posting provides evidence for discussion of the problem in this case, probable cause, solution, and a better design to prevent the problem.

Analysis

The type of programmer (Arduino), connection (COM port) are the settings one would use to talk to a bootloader already installed on the mcu to write the application program to flash. They are not the settings one would use to install the bootloader, they are not suitable for talking to the ISP facility burned into silicon. Continue reading (tr)uSDX bootloader corruption – a smoking gun

Last update: 27th July, 2022, 6:50 AM

Digital display for DIY 25W dummy load – part 2

Digital display for DIY 25W dummy load – part 1 described VK4MQ’s build of a DIY 25W dummy load / digital wattmeter with very good performance. As part of the project, Bruce made an exhaustive set of measurements of Prf vs Vdc from 0.001W to 25W. A second order curve fit was calculated and is used in the instrument to transform measured Vdc to Prf for display.

That project was an elaboration of a design worked up at Digital display for QRP labs 20W dummy load – part 1 and following articles. That workup included an LTSPICE model of the half wave detector with BAT46 diode, 0.1µF capacitor and 56k+1k voltage divider. A second order curve fit was calculated and is used to transform measured Vdc to Prf for display.

This article compares the LTSPICE model data set, its curve fit, the measurements of Bruce’s implementation, and its curve fit. Continue reading Digital display for DIY 25W dummy load – part 2

Last update: 20th August, 2022, 6:05 AM

Digital display for DIY 25W dummy load – part 1

Digital display for QRP labs 20W dummy load – part 1 and following articles laid out a initial study into the feasibility of an approach of a similar project. This project uses the same display solution for a DIY 25W dummy load / digital wattmeter with very good performance.

This article describes Bruce, VK4MQ’s, build.

Implementation

Bruce built the dummy load wattmeter into a small die cast box.

Above, the front panel view, the OLED display shows power in watts and dBm, and a bar chart display. The unit is battery powered, and has a on/off switch on the front panel. Continue reading Digital display for DIY 25W dummy load – part 1

Last update: 21st February, 2023, 7:29 AM

NanoVNA source mismatch error

One of the popular ideas online is that the correction process in the NanoVNA does not correct errors in mismatch at Port 1 and Port 2. This article deals with the first case ONLY, Port 1 mismatch.

An experiment with source VSWR nominally 2:1

A NanoVNA was configured with a SMA tee connected to Port 1 and a good 50Ω termination connected to the branch port, see the pic below. The left hand side of the tee becomes the new Port 1 interface, and by virtue of the additional 50Ω shunt termination, if the native Port 1 was indeed well represented by a Thevenin equivalent circuit with Zs close to 50+j0, the Thevenin source impedance is now closer to half that, Zs close to 25+j0.

Some would calculate this mismatch as causing a mismatch loss of 0.512dB that is additional loss in the s21 path.

Above is the test setup. The NanoVNA was SOLT calibrated with cal parts attached to the left hand side of the tee and the 200mm coax jumper from that point to Port 2. Continue reading NanoVNA source mismatch error

Last update: 6th July, 2022, 9:15 AM

Trying to make sense of Nanosaver’s R/ω and jX/ω graph

Nanosaver v0.4.0 contains a graph that I have found difficult to understand, much less find application.

Above is the graph scaled R/ω and jX/ω, and an untitled X axis, though it would appear to be frequency in Hz (scaled by the M multiplier).

I had difficulty reconciling the Y values plotted for R/ω and jX/ω with the displayed R,jX values.

David F4HTQ offers the following explanation online.

I add some explanations.

I asked Rune if he could add this graphic because it is very useful.
It display curves that have exactly the same shape as the complex permittivity curves (μ’r and μ”r) of the ferrite datasheets.

The values do not match those of the constructor curve ( to have the right value the software might know the exact geometry of the inductor) , but the shape is absolutely identical.

This allow to easy identify unknown ferrite core, and to better understand how to use it in a RF device.

He says permittivity… but he is talking about permeability.

The quote seems to say the Y axis scale is worthless?

In any event, the underlying R,X data only follows µ at frequencies well below the self resonant frequency (SRF) of the inductor.

Let’s try a measurement

Continue reading Trying to make sense of Nanosaver’s R/ω and jX/ω graph

Last update: 6th July, 2022, 3:10 AM

Digital display for half wave detector with cubic spline interpolation – part 4

Digital display for half wave detector with cubic spline interpolation – part 1 and following articles laid out the design concepts of a power meter display.

Digital display for half wave detector with cubic spline interpolation – part 2 described a simple cubic spline interpolation model.

This article examines the problem a little deeper to arrive at an improved solution.

The chart above compares the response of an ideal peak detector (cyan) with an LTSPICE simulation of a BAT46 with 57kΩ load (orange x). Whilst the simulation approaches the ideal at peak RF voltage Vp greater than 3V, it departs greatly at very low Vp. Continue reading Digital display for half wave detector with cubic spline interpolation – part 4

Last update: 3rd July, 2022, 6:20 PM

Becen 25W type N dummy load

 

I purchased an inexpensive 50Ω dummy load rated at 25W from Becen on Aliexpress (~$20 inc shipping), the intended application is HF.

Above, the dummy load.

Above, the centre pin passes a gauge test, doesn’t satisfy the Precision N criteria, but well within tolerance of non-precision N connectors. Continue reading Becen 25W type N dummy load

Last update: 2nd July, 2022, 12:45 PM

Digital display for half wave detector with cubic spline interpolation – part 3

Digital display for half wave detector with cubic spline interpolation – part 1  and following articles laid out the design concepts of a power meter display.

Whilst the preferred target was an Arduino Zero (SAMD21G) for its 32bit architecture, speed, and 12bit ADC, the code was developed to run on a Zero or a Arduino Nano (ATmega328P).

This article explores a trial of an external ADC module using an ADS1115 chip, 4 channels 16bit +/- ADC.

Above is the prototype, Arduino Nano on the left,  the ADS1115 module is to the right of the display. Continue reading Digital display for half wave detector with cubic spline interpolation – part 3

Last update: 4th July, 2022, 10:07 AM

Implementation of G5RV inverted V using high strength aluminium MIG wire – 5 year review

This article continues on from Implementation of G5RV inverted V using high strength aluminium MIG wire documenting review after 5 years operation under a wide range of temperature, humidity and wind conditions.

Above is a view of the steel mast with the Inverted V G5RV rigged from the top of the 11m mast using a halyard though a purchase on a small gibbet to offset the antenna and feed line from the mast. There are lateral guys at 7m height, and the left hand one is non-conductive synthetic fibre rope. Atop the mast is a 2m/70cm vertical. Continue reading Implementation of G5RV inverted V using high strength aluminium MIG wire – 5 year review

Last update: 30th June, 2022, 3:49 PM